The present invention relates, in general, to a plasticizing barrel, and to a method of making such a plasticizing barrel.
Plasticizing barrels are used to plasticize granular plastic material in an injection assembly or an extruder by means of a screw for a subsequent injection process. As the inner wall of the plasticizing barrel is subject to great stress during plasticizing, it has been commonly proposed to line the inner wall with a wear-resisting coating. The application of such a wear-resisting coating may be implemented by a so-called centrifugal casting process in which metallic powder is introduced into a rotating hot hollow-cylindrical body, pressed against the inner barrel wall as a consequence of centrifugal forces, and melted there. After a cool-down period, the thus produced layer on the inside wall exhibits a fairly good surface quality and requires only little finishing works.
When more powerful plasticizing units are involved, barrels with grooves are required whereby the grooves extend almost over the entire length of the plasticizing barrel. These barrels do not have a wear-resisting protective layer; rather, barrel blanks are formed in “soft state” with the grooves, and subsequently the inner barrel wall is hardened by a nitriding process.
It is also known to place so-called grooved bushings in the feed zone of plasticizing units for improving the transport of introduced raw plastic material. These grooved bushings are normally also coated for wear-resistance, e.g., through a high-temperature isostatic pressing process. The wear-resisting protective layer of the grooved bushing can be provided either directly into the plasticizing barrel, or the grooved bushing can be produced separately and subsequently placed into the plasticizing barrel. This process is applicable only for relatively short grooves.
It would therefore be desirable and advantageous to provide for a plastics processing machine an improved plasticizing barrel which obviates prior art shortcomings and which includes an inner coating and exhibits on its inner wall a groove or grooves.
It would also be desirable and advantageous to provide an improved method of making such a plasticizing barrel.